HIGH ldap injectionginbearer tokens

Ldap Injection in Gin with Bearer Tokens

Ldap Injection in Gin with Bearer Tokens — how this specific combination creates or exposes the vulnerability

LDAP Injection is an injection vector that occurs when an application passes unsanitized user input into LDAP query building logic. In a Gin-based Go service that uses Bearer Tokens for authentication, the vulnerability typically arises not from the token itself, but from how the application uses data extracted from the token or from other request sources to construct LDAP filters.

Bearer Tokens are often validated via an identity provider, and the claims (such as username, email, or groups) are extracted and used in downstream operations, including LDAP queries for authorization or user lookups. If these claims are directly concatenated into an LDAP filter without proper escaping, an attacker can manipulate the token’s claims (for example, by providing a malicious username during token issuance or by exploiting a misconfigured token endpoint) to alter the LDAP query logic.

Consider a Gin handler that retrieves the username claim from a Bearer Token and uses it in an LDAP filter like this:

username := claims["username"].(string)
filter := fmt.Sprintf("(&(objectClass=user)(uid=%s))", username)

An attacker who controls the username claim could supply admin)(uid=attacker as the username, turning the filter into:

(&(objectClass=user)(uid=admin)(uid=attacker))

This changes the query semantics and may return unauthorized entries or bypass intended access controls. In the context of middleBrick scanning, this pattern would be flagged under BOLA/IDOR and Input Validation checks because the application fails to enforce strict separation between query structure and user data. The scan would highlight that unescaped input is being used to construct LDAP filters, which can lead to unauthorized data access or authentication bypass.

Additionally, if the Gin application exposes an unauthenticated endpoint that accepts an LDAP filter as a query parameter and passes it directly to an LDAP search, this would compound the risk. middleBrick’s LLM/AI Security checks would not apply here because this is not an LLM-related issue, but the Input Validation and Property Authorization checks would identify the absence of input sanitization and improper authorization checks.

Real-world LDAP injection patterns are well documented in the OWASP Testing Guide and map to the OWASP API Top 10 category: Broken Object Level Authorization (BOLA). When using Bearer Tokens, ensure that any data derived from token claims is treated as untrusted input and is escaped or parameterized before inclusion in LDAP queries.

Bearer Tokens-Specific Remediation in Gin — concrete code fixes

Remediation focuses on strict input validation, parameterized queries, and avoiding string concatenation when building LDAP filters. In Go, use the github.com/go-ldap/ldap/v3 package which provides helper functions to construct filters safely.

First, validate and sanitize the username claim. Do not trust any data derived from the token. Use a whitelist approach for acceptable characters and length.

Second, use the library’s filter building functions instead of fmt.Sprintf. Here is a secure example:

import (
    "github.com/gin-gonic/gin"
    ldap "github.com/go-ldap/ldap/v3"
)

func handleLDAP(c *gin.Context) {
    claims, exists := c.Get("claims")
    if !exists {
        c.AbortWithStatusJSON(401, gin.H{"error": "missing claims"})
        return
    }
    username, ok := claims.(map[string]interface{})["username"].(string)
    if !ok || username == "" {
        c.AbortWithStatusJSON(400, gin.H{"error": "invalid username claim"})
        return
    }

    // Safe: use ldap.FilterEncodeValue to escape special characters
    filter := ldap.Filter{Attributes: []string{"objectClass", "uid"}}
    filter.Equal("uid", username)

    // Alternatively, build a filter string safely
    safeFilter := ldap.BuildFilter("(uid=%s)", ldap.EscapeFilter(username))

    conn, err := ldap.DialURL("ldap://example.com")
    if err != nil {
        c.AbortWithStatusJSON(500, gin.H{"error": "ldap connection failed"})
        return
    }
    defer conn.Close()

    searchReq := ldap.NewSearchRequest(
        "dc=example,dc=com",
        ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
        safeFilter,
        []string{"dn"},
        nil,
    )
    sr, err := conn.Search(searchReq)
    if err != nil {
        c.AbortWithStatusJSON(500, gin.H{"error": "ldap search failed"})
        return
    }
    c.JSON(200, gin.H{"entries": sr.Entries})
}

In this example, ldap.EscapeFilter ensures that characters like (, ), *, and \ are escaped, preventing injection. Avoid using raw string formatting to build filters. Also, ensure that token validation is performed strictly and that claims are type-asserted safely before use.
For production, combine this with rate limiting and monitoring for anomalous LDAP query patterns. middleBrick’s CLI can be used in CI/CD to verify that your endpoints do not exhibit input validation weaknesses related to LDAP construction. Run middlebrick scan <url> to validate the behavior of your Gin endpoints.

Frequently Asked Questions

Why does using Bearer Token claims in LDAP queries require escaping even though tokens are signed?

Tokens are signed to ensure integrity and authenticity, but the claims they carry are untrusted input from the perspective of the application. An attacker may present a malicious token or exploit a token issuance flaw to inject crafted values. Escaping ensures that special LDAP characters in the claims cannot alter the query structure.

Does middleBrick test for LDAP injection in APIs that use Bearer Tokens?

Yes. middleBrick runs Input Validation and Property Authorization checks that include scenarios where token-derived data is used in backend queries such as LDAP. The scanner does not require authentication and tests the unauthenticated attack surface to identify injection risks.

Ldap Injection in Gin with Bearer Tokens